1. Technical Field
The present invention relates to structures and methods for fabrication of a magnetoresistive random access memory (MRAM) device, and more particularly to MRAMs with a read and write field line that utilizes an armature-like magnetic cladding to increase the magnetic field generated per unit current to decrease power of read and write operations, and enable denser memory arrays with read/write field drivers (transistors).
2. Description of the Related Art
Thermally-assisted magnetoresistive random access memory (TAS-MRAM) heats a magnetic tunnel junction stack (MTJ) to a write temperature (Twrite) higher than a maximum storage temperature (Tstore) to write to the device. The device includes a storage magnetic layer, and a sense magnetic layer, separated by a non-magnetic tunnel barrier. Electrical resistance of this stack depends on the relative orientation of portions of the storage and sense layers that interface with the tunnel barrier. This effect is caused by a tunneling magnetoresistance (TMR) phenomenon. In typical devices, an antiferromagnetic layer pins the storage layer at TMTJ<Tstore where TMTJ is the magnetic tunnel junction stack temperature, and Tstore is the storage temperature. The sense magnetic layer is free to toggle back and forth by an applied field.
If the magnetic orientation of the sense layer is parallel to the magnetic orientation of the storage layer, then the MTJ stack will have low resistance; if the sense layer is anti-parallel to the storage layer, the stack will have high resistance. The device is read out by toggling the sense layer in both directions by an applied field of two known directions, and determining the direction of the storage layer based on the resistance change.
To write the device into a logical “1” or “0” state, a heating current is passed through the device in order to raise TMTJ>Twrite, which depins the storage layer by suppressing the antiferromagnetism in the antiferromagnetic pinning layer, allowing an applied field to reset the storage layer magnetization into the “1” state direction, or to the “0” state direction. The storage layer may include a single magnetic layer, or a synthetic antiferromagnetic layer; each of these magnetic layers may, in turn, include several distinct alloys, compound materials and material layers. In all cases, the write operation requires reorienting the magnetization of the layer interfacing with the barrier to either the “1” or “0” state direction.
To read the device or write the device into a logical “1” or “0” state, a field must be applied from a current-carrying metal wire located close to the device. Conventional structures often consume a large amount of power using this field line to create sufficient field generated per unit current in the field line during read and write operations.